Various types of radar systems are used in government and military applications, such as for early warning devices that show the approach of aircraft, missiles, ships, and land vehicles. Conventionally, a flat, circular CRT serves as the radar display, showing dots or “blips” for detected objects, updated with each sweep of the radar signal. Fiducial “rings” on the CRT surface help to indicate range increments. For many types of applications, this type of two-dimensional display has proved sufficiently usable for skilled operators who can interpret the displayed data.
Civilian air traffic control systems also use radar as a means for tracking and guiding aircraft movement. For this type of application, however, the limitations of the conventional CRT display are most readily apparent. Two dots appearing on the flat CRT screen may indicate aircraft that are at very different altitudes, for example. It requires highly skilled personnel to interpolate between the limited scope of the radar display CRT and the three-dimensional, real-world objects that are represented, particularly since the tracked objects are in motion. As air traffic continues to grow in volume, there are increased risks for mistakes that can jeopardize life and property.
Although the CRT only represents two-dimensional data, the radar system itself actually obtains three-dimensional data on detected moving objects. As shown in FIG. 1A, the radar scan from a radar scanner 10, directed along a cone 26, provides information on elevation and azimuth angle A for detected objects such as aircraft 12. In addition, transponder apparatus 14 on each aircraft 12, often incorporating Global Positioning System (GPS) capabilities, provide information such as altitude and air speed. Thus, with no change to existing radar tracking systems, there is already sufficient information available to locate an airborne object within a volume in a cylindrical coordinate system 20 as shown in FIG. 1B, with fiducial rings 16 for altitude, such as one every 5,000 feet, for example. However, as FIG. 1C shows, a conventional CRT radar display 18 shows only blips 22 that correspond to aircraft 12 position. Conventional radar display 18 is unable to show elevation data graphically; instead, many systems display text information about altitude and air speed next to each blip 22. Thus, the data displays in a compressed manner, as if the observer were looking downward on the cylindrical space of FIGS. 1A and 1B. As a further drawback, conventional display methods do not indicate aircraft 12 direction on an instantaneous basis; this data must be inferred from observation.
There have been a number of solutions proposed for stereoscopic and three-dimensional imaging that can be used in radar avionic applications. For example:                U.S. Pat. No. 4,805,015 (Copeland) discloses the use of widely spaced sensors on a plane for providing left- and right-images for improved depth perception of another aircraft or object;        U.S. Pat. No. 5,825,540 (Gold et al.) discloses a pupil-based autostereoscopic display for viewing an object from multiple locations; and        U.S. Pat. No. 6,208,318 (Anderson et al.) discloses a display for a volumetric image, supplemented by a two dimensional display.        
It can be appreciated that there would be significant benefits to a display system that provided a stereoscopic, three-dimensional view of radar and tracking system data. Equipped with such a display, an air traffic controller could be provided with a view of the full volume of air space around an airport, for example. Such a display could use data from a single radar system to render a viewable stereo representation, rather than requiring that two separate radar systems provide two separate image sources, as is typically needed for conventional stereo image forming apparatus.